Carbon dioxide extruded pellets

ABSTRACT

Apparatus for producing carbon dioxide extrusions such as pellets by flashing carbon dioxide liquid to form carbon dioxide snow and vapor in a chamber. A reciprocating piston in the cylinder compresses the snow material and extrudes compacted carbon dioxide snow through extrusion orifices at one end of the chamber. The chamber is constructed with openings in the lateral wall to permit part of the snow to be ejected therethrough into a snow retaining box, the snow in the box being employed as a porous filter to separate the vapor from the snow within the chamber.

United States Patent [1 1 Scudder CARBON DIOXIDE EXTRUDED PELLETS [75]Inventor: John A. Scudder, Homewood, 111.

[73] Assignee: Chemetron Corporation, Chicago,

22 Filed: Oct. 26, 1971 21 Appl. No; 192,138

[4 1 Sept. 17, 1974 3,618,330 11/1971 Hardt 62/35 3,660,986 5/1972 Hardt62/35 FOREIGN PATENTS OR APPLICATIONS 353,014 7/1934 England 62/10642,057 4/1928 France 62/10 Primary Examiner-Norman Yudkoff Attorney,Agent, or Firm-N. M. Esser [57] ABSTRACT Apparatus for producing carbondioxide extrusions such as pellets by flashing carbon dioxide liquid toform carbon dioxide snow and vapor in a chamber. A reciprocating pistonin the cylinder compresses the snow material and extrudes compactedcarbon dioxide snow through extrusion orifices at one end of thechamber. The chamber is constructed with openings in the lateral wall topermit part of the snow to be ejected therethrough into a snow retainingbox, the snow in the box being employed as a porous filter to separatethe vapor from the snow within the chamber.

1 Claim, 9 Drawing Figures [52] US. Cl. 62/35, 62/10 [51] Int. Cl F25jl/00 [58] Field of Search 62/10, 35, 14

[56] References Cited UNITED STATES PATENTS 1,894,892 l/1933 Small 62/351,912,445 6/1933 Goosmann 62/10 1,989,873 2/1936 Marcus 62/35 2,011,5518/1935 Hasche 62/10 2,153,629 4/1939 Kobold 62/10 2,999,364 9/1961Hellingman 62/14 3,077,081 2/1963 Schnoor 62/10 3,162,517 12/1964Verbeek 62/14 3,576,112 4/1971 Frost 62/35 24 ENIEUSEPI 719 PM F 3 SHEU3 0 CARBON DIOXIDE EXTRUDED PELLETS This invention relates to apparatusfor making pellets, and particularly to apparatus for continuouslymaking carbon dioxide pellets.

Prior art discloses apparatus for automatically making carbon dioxideextrusions such as pellets. The prior art also discloses apparatuswherein carbon dioxide snow is formed within a chamber by flashingcarbon dioxide liquid into the chamber and a portion of the snow soformed serves as a porous filter. The invention disclosed herein is animprovement in such apparatus and in a related method for producingcarbon dioxide extrusions, to make more efficient use of the snow itselfas a porous filter than previously have been known to the art. US. Pat.No. 3,576,112 and United States Pat. No. 3,6l8,330, which are assignedto the assignee of this application, disclose carbon dioxide pelletmaking apparatus as referred to above.

Briefly summarized, the invention herein provides improved apparatus andan improved method for producing carbon dioxide extrusions andexpecially for making more efficient use of carbon dioxide snow as amedium for filtering carbon dioxide vapor also formed during theproduction of such extrusions. In the apparatus, one or more openingsprovided in a snow barrel communicate with a snow retaining box mountedexternally of the snow barrel. Reciprocation of a piston in the snowbarrel fores snow through the openings into the snow retaining box suchthat snow is compacted therein to form a porous filter. A porous matrixpreferably in the form of a screen is included in a wall portion of thesnow retaining box and permits carbon dioxide vapor to be vented.

IN THE DRAWINGS FIG. I is a perspective view showing a pair of apparatusfor producing carbon dioxide extrusions;

FIG. 2 is an elevation view of one of the apparatus of FIG. 1, partiallybroken away, showing a piston in a retracted position;

FIG. 3 is a view, similar to FIG. 2, showing the piston in an advancedposition;

FIG. 4 is a view of a cylinder or snow barrel of said apparatus with asnow retaining box mounted thereon;

FIG. 5 is an end view of the snow barrel and snow retaining box of FIG.4;

FIG. 6 is a plan view of the apparatus of FIGS. 2 and 3 showing the snowretaining box and attached filter covers;

FIG. 7 is an enlarged sectional view ofa detail of FIG. 6 showing thefilter screen arrangement;

FIG. 8 is a detail ofthe snow barrel showing injectors and theirposition in relation to openings in the cylinder wall; and

FIG. 9 is a detail of an injector of FIG. 8.

Referring now to the drawings, in which like reference characters in theseveral views designate similar parts, the numeral 10 designatesgenerally apparatus for producing carbon dioxide extrusions such aspellets. The apparatus 10 includes a cylinder or snow barrel 12, anextrusion piston 14 disposed in the snow barrel. hydraulicpiston-actuating mechanism 16, an orifice plate or head 18 secured atone end of the cylinder through which compacted carbon dioxide snow isextruded and a filter manifold 20 associated with the snow barrel. Oneor more apparatus 10 may be mounted on a cabinet as shown, adapted tohouse controls associated with the apparatus 10 for its or theiroperation.

The cylinder or snow barrel 12 is secured between the orifice plate 18at one end and a cylinder mounting plate 22 at the other end by aplurality of tie rods 24. The plate 22 forms the back face of the snowbarrel l2. Plural openings 26 are arranged circumferentially around thelateral wall of the snow barrel 12 for a purpose to be hereinafterexplained. As shown, the openings 26 extend over major portions of thecircumference of the lateral wall of the snow barrel 12. Injector tubes28, which extend through the lateral wall of the snow barrel 12, areadapted to be connected to a source of carbon dioxide liquid forinjection into the chamber C in the snow barrel 12. The extrusion piston14 is disposed in the snow barrel 12 for reciprocating movement therein.

The hydraulic piston-actuating mechanism 16 is arranged to provide timedactuation of the piston 14 in the snow barrel. The piston-actuatingmechanism herein illustrated includes a cylinder 30 and a double actingram 32 therein which extends through the cylinder mounting plate 22 andis secured to the piston 14 preferably at a threaded connection as shownat 34. The cylinder 30 is secured between mounting plates 36 and 38 by aplurality of tie rods 40 with the mounting plate 38 being secured to thecylinder mounting plate 22. Hydraulic fluid connections 42 and 44 areprovided to communicate with respective ends of the cylinder 30 wherebyactuation of the ram 32 and the extrusion piston 14 connected thereto isachieved.

The orifice plate 18 secured at one end of the snow barrel 12 has formedtherein a plurality of orifices 46 through which compacted carbondioxide snow is extruded. The filter manifold 20 includes a snowretaining box 48 mounted to the outside of the snow barrel 12 to enclosethe openings 26 in the snow barrel 12. The snow retaining box 48comprises a substantially rectangular box-like structure including upperand lower plates 50 and 52 and interconnecting side plates 54 and 56through which the snow barrel 12 extends. Wall portions respectivelycomprising a frame 58 and a porous matrix preferably in the form of afilter screen 60 therein are disposed at each end of the snow retainingbox to complete the box-like structure. Box-like filter covers 62 and 64are attached by suitable means such as bolts 66 to the snow retainingbox 48 to complete the manifold 20. Vent tubes 68 attached to each ofthe filter covers provide means whereby the filtered vapor may beconducted to appropriate apparatus (not shown) for reliquefaction asdescribed in the above referred to US. patents. The snow retaining box48 retains carbon dioxide snow which acts as a porous filter for carbondioxide vapor formed in the chamber C. As the piston 14 reciprocates inthe snow barrel 12, the piston 14 forces carbon dioxide snow formed inthe chamber C through the openings 26 to compact the snow in the snowretaining box 48.

Carbon dioxide liquid under pressure is flashed into the chamber Cthrough the injectors 28. Thus, carbon dioxide snow and vapor are formedin the chamber C. As the piston 14 is reciprocated by the pistonactuating mechanism 16, the piston 14 advances from a retracted positionas shown by dotted lines in FIG. 2 to a fully advanced position as shownin FIG. 3. It will be observed from FIG. 2 that piston 14 in its fullyretracted position leaves the openings 26 in the cylinder 12 fullyexposed. As snow forms in the chamber C upon the flashing of carbondioxide liquid, a portion of the snow is forced through the openings 26into the snow retaining box 48, and the snow is compacted in the snowretaining box. Thus, the snow therein forms a porous filter 70 for thevapor formed in the chamber C. As the piston 14 advances, it formsadjacent the orifice plate 18 a plug 72 of compressed carbon dioxidesnow. The plug 72 provides a seal between the atmosphere and the chamberC. Thus carbon dioxide vapor in the chamber C is removed from thechamber C by passing through the snow filter in the snow retaining box48 and then through the filter screens 60 and into the vent conduits 68.Also, as the piston 14 advances, the snow in chamber C is compacted, anda portion of the compacted carbon dioxide snow is extruded through theorifices 46. Then, the remaining compacted carbon dioxide snow reformsthe plug 72.

in the apparatus 10, the preferred orientation is for the central axisof the snow barrel 12 to be horizonal, as shown. However, thearrangement of the snow filter in the apparatus It) enables theapparatus to be operated, as described, without reference to gravity.

It has been found that the presence of carbon dioxide liquid in thechamber C should be avoided. Particularly, it has been found that suchliquid flashes to carbon dioxide vapor as the compacted snow is beingextruded and thus tends both to fragment the pellets and to ejectfragmentary pellets explosively from the orifices 46. Thus, it has beenfound highly desirable to operate the apparatus 10 to insure that thevapor pressure within the chamber C does not exceed the triple-pointpressure as carbon dioxide liquid is flashed to form carbon dioxide snowand vapor in the chamber C.

The venting of carbon dioxide vapor is restricted at the openings 26, atthe compacted snow in the snow box 48, at the filter screens 60, anddownstream of the filter screens 60. These restictions tend to cause thevapor pressure to be increased in the chamber C as carbon dioxide liquidis flashed to form carbon dioxide snow and vapor in the chamber C.

The vapor pressure within the filter covers 62 and 64 downstream of thefilter screens 60 may be measured by conventional means (not shown) andin the apparatus 10 generally is approximately equal to atmosphericpressure. The pressure of the hydraulic fluid which actuates the ram 32and thereby actuates the piston 14, may be measured by conventionalmeans (not shown). Such pressure serves as a measure of the compactingpressure within the chamber C. Also, it provides an indication of thecompacting pressure within the snow box 48 so long as the openings 26are exposed.

It has been found that the permeability of carbon dioxide snow to carbondioxide vapor is related to the density of the snow and thus to thepressure with which the snow is compacted. Thus, in order to operate theapparatus 10 such that the vapor pressure within the chamber C does notexceed the triple-point pressure as carbon dioxide liquid is flashed toform carbon dioxide snow and vapor in the chamber C, it has been foundnecessary to control the maximum density of the snow in the snow box 48by controlling the maximum compacting pressure within the snow box 48.

From the drawings, it is evident that the advancing piston 14 compactsthe snow both in the chamber C and in the snow box 48 so long as theopenings 26 are exposed and that it compacts the snow only in thechamber C once the openings 26 are blocked by the piston 14. Thus, theposition of the openings 26 along the snow barrel 12 controls thecompacting pressure within the snow box 48 and thus controls the densityof the snow in the snow box 48 such that the vapor pressure within thechamber C does not exceed the triplepoint pressure as carbon dioxideliquid is flashed to form carbon dioxide snow and vapor in the chamberC. Also, while the apparatus 10 is operating with compacted snow in thesnow box 48, the filter covers 62 and 64 and the filter screens 60 maybe removed, as for cleaning or replacement, without loss of thecompacted snow in the snow box 48.

Moreover. from the drawings, it is evident that the total area of theopenings for the filter screens 60 is larger than the total area of theopenings 26. Thus, the pressure increase caused by the filter screens 60is less than it would be if smaller screens (not shown) of the samemicron-size were to be employed merely to cover the openings 26.

By way of an example, an apparatus similar to the apparatus 10 has beenconstructed and successfully oper ated with the following approximatedimensions:

Piston: 8 inches dia. X ll' /sinches length. 20 inches travel;

Snow barrel: 8 inches inner dia. X ZZVzinChes length;

Openings (8) from snow barrel to snow box: 2 /2inches sq.. back edgesl2l sinches from back face of snow barrel:

lnjection Orifices (2): center lines 1 l /sinches from back face of snowbarrel (at outside of snow barrel). five-sixteenths inch inner dia. atinlet, Z'Vsinches long, 6 taper, 40 angle to axis of snow barrel;

Extrusion Orifices (86): /2inch dia. (nominal) Snow Box: 13%inchesscreen-to-screen, (2) screen openings 8%X 4 inches ea., 32 micronsizestainless steel cloth filter screens.

(Note: figures in parentheses refer to the quantities of the features.)

Such apparatus was successfully operated at one cycle per 48 seconds,with the hydraulically driven piston advancing 10 inches in l6 secondsand reacting fully in 8 seconds. Carbon dioxide liquid at 200 psi. -l0F,was injected throughout a 24-second period during which the piston wasin its retracted position, at a rate of 17 pounds-total per cycle, toform about 50 percent snow and about 50 percent vapor in the chamber ofthe snow barrel, the vapor pressure within the chamber remaining below50 psig. The snow barrel achieved an average temperature of-l 10F. Snowsublimed in the snow box was replenished from compacted snow in thechamber. (The foregoing data are illustrative.)

During the advance ofthe piston, the data of TABLE I was obtained asillustrative of the novel timed sequence of this invention.

TABLE I EXTRUDER OPERATlON TIME TABLE I-Continued EXTRUDER OPERATIONTIME PISTON TRAVEL PRESSURE, PRESSURE Legend Time in seconds, pistontravel in inches, pressures in psig; PRESSURE =hydraulic fluid pressuremeasured; PRESSURE pressure ofthe piston on the snow in the chamber,calculated from P,A,=P A where A and A are the areas respectively of theram and the piston.

(Note: A block was applied externally to seal the extrusion orificesuntil a plug of compacted carbon dioxide snow was formed internally atthese orifices.)

Thus, it will be appreciated that all of the recited objects, advantagesand features of this invention have been demonstrated as obtainable in ahighly practical apparatus and one that is simple and positiveinoperation. It will be further understood that although this inventionhas been described with respect to certain specific embodiments thereof,this invention is not limited thereto. since various modifications ofsaid invention will suggest themselves from the aforesaid descriptionand are intended to be encompassed within the scope of the appendedclaims wherein there is claimed.

I claim:

1. ln apparatus for producing carbon dioxide extrusions of the typecomprising a barrel having a generally tubular lateral wall and defininga generally cylindrical chamber adapted to receive carbon dioxide snowand vapor, said chamber having at least one extrusion orifice, means forflashing carbon dioxide liquid to form carbon dioxide snow and vapor insaid chamber, means including a piston reciprocable in said chamber forcompacting carbon dioxide snow in said chamber to extrude a portion ofthe compacted snow through the extrusion orifice, and means for removingcarbon dioxide vapor from said chamber, the improvement wherein saidmeans for removing carbon dioxide vapor from said chamber comprises asnow retaining box mounted externally of and to the lateral wall of saidbarrel to enclose plural openings in said lateral wall, said openingsbeing arranged circumferentially around and extending over majorportions of the circumference of said lateral wall, said box beingadapted to receive and retain carbon dioxide snow, an outer wall portionof said box including a porous matrix larger in area than the openingsin the lateral wall of said barrel and disposed externally of saidlateral wall, said matrix being adapted to retain carbon dioxide snow insaid box and to pass carbon dioxide vapor from said box, and a filtercover removably mounted on said box so that said cover and said matrixmay be removed from said box without loss of snow from the apparatus,said cover being disposed over said matrix to receive the vapor passingfrom said box.

